
I agree with the others it rteally varies from litter to litter. I have started pups on solids as soon as their eyes have been open when they seemed restless and hungry, and have had trouble getting much interest in food before 4 1/2 weeks with others.
I usually try to start them at about 18 days to 3 weeks, just a taste of soaked puppy food with puppy milk once a day at first, and depending on how keen they are offer the same over more occasions building to 4 times a day gradually increasing the amount with their appetite.
Mum gets to finish the food they played with :D